QCD Results from the Tevatron Kenichi Hatakeyama 畠山 賢一 Baylor University Aspen Particle Physics Conference Aspen Center of Physics January , 2010

January 18, Outline  Fermilab Tevatron, CDF and D0 Detectors  Inclusive jets and dijets  Photons  W/Z+jets  Soft QCD and Exclusive Production  Summary & Remarks Only a small fraction of extensive QCD results from the Tevatron can be covered in 20 minutes. More results can be found on:  

January 18, Fermilab Tevatron >7 fb-1 delivered (Run I: 120 pb-1) Batavia, IL Tevatron Main Injector World’s highest energy “proton-antiproton” collider Most likely to run until FY2011

January 18, CDF and DØ CDF & DØ running well and recording physics quality data with high efficiency (85-90 %) Both experiments have already collected > 6 fb-1 on tape

Inclusive Jets & Dijets α s, PDFs, Physics beyond the Standard Model

January 18, Jet Production at the Tevatron  Test pQCD at highest Q 2.  Unique sensitivity to new physics Compositeness, new massive particles, extra dimensions, …  Constrain PDFs (especially gluons at high-x)  Measure α s Hard Scatter PDFs jet underlying event

January 18, Inclusive Jet Cross Section  Measurements span over 8 order of magnitude in dσ 2 /dp T dy  Highest p T jet > 600 GeV/c p T (GeV/c) Phys. Rev. D 78, (2008) p T (GeV/c) Phys. Rev. Lett. 101, (2008)

January 18, Inclusive Jet Cross Section  Both CDF and D0 measurements are in agreement with NLO predictions Both in favor of somewhat softer gluons at high-x  Experimental uncertainties: smaller than PDF uncertainties  Discussions on the impact to PDF in a different talk CTEQ6.5M PDFs p T (GeV) see also, Inclusive jets with Kt, CDF, Phys. Rev. D 75,

January 18, Strong Coupling Constant From 22 (out of 110) inclusive jet cross section data points at 50 < p T < 145 GeV/c · NLO + 2-loop threshold corrections · MSTW2008NNLO PDFs · Extend HERA results to high p T % precision Phys. Rev. D 80, CDF results in Phys. Rev. Lett. 88,

January 18, Dijet Mass Spectrum  Test pQCD predictions  Sensitive to new particles decaying into dijets: excited quarks, heavy gluons, techni-ρ, etc Dijets with jets |y jet |<1 Consistent with QCD - no resonance Most stringent limits on many new heavy particles Mass reach up to ~ 1.2 TeV/c 2 Limits: σ B A(|y jet |<1) (pb) Phys. Rev. D 79,

January 18, Dijet Mass Spectrum D0 measurement goes to forward rapidity regions  six |y max | regions (0<|y max |<2.4)  PDF sensitivity at large |y max |  Favor softer high-x gluons  No indications for resonances M jj (TeV/c 2 ) Data / Theory D0 Conf Note 5919

January 18, Dijet Angular Distribution Dijet Angular Distribution  Consistent with NLO pQCD  Limits on Compositeness & LED Quark Compositeness Λ > 2.9TeV ADD LED (GRW) Ms > 1.6 TeV TeV-1 ED Mc > 1.6 TeV Phys. Rev. Lett. 103, θ*θ* θ*θ* quark compositeness extra dimensions Also CDF results in CDF public note 9609

Photons Photons: “direct” probes of hard scattering Test perturbative QCD, PDFs

January 18, Inclusive Photon Cross Sections  Data/NLO pQCD: In agreement at high p T, but enhancement at low p T  D0 measurement shows similar trends (Phys. Lett. B 639, 151) Similar shape also in Run 1 analyses – need to be understood Directly sensitive to hard scatter Phys. Rev. D80, (2009)

January 18, Photon + HF Jet Production  Sensitive to HF-content of proton  Bkgd for many BSMs Photon p T : 30 – 150 GeV/c Rapidities: |y  |<1.0, |y jet |<0.8 Photon+b:  Agreement over full p T  range Photon+c:  Agree only at p T  <50 GeV/c.  Disagreement increases with p T .  Using PDF including the intrinsic charm (IC) improves, but p T  (GeV/c) data and theory still not compatible Phys. Rev. Lett. 102,

Vector Boson + Jets Prerequisites for top, Higgs, SUSY, BSM Test perturbative QCD calculations & Monte Carlo Models

17 W/Z+Jets Production  W/Z+jets are critical for physics at the Tevatron and LHC: top, Higgs, SUSY, and other BSM  NLO pQCD calculations are available up to 2(3) jets  Many Monte Carlo tools are available LO + Parton shower Monte Carlo (Pythia, Herwig, ) MC based on tree level matrix element + parton showers, matched to remove double counting: Alpgen, Sharpa, …  These calculations and tools need “validation” by experimental measurements January 18, 2010

18 Z+Jets Production Data and NLO pQCD in agreement Phys. Rev. Lett 100, & update Good control sample for SUSY search

January 18, Z + (1, 2, 3) Jets Testing Monte Carlo Models: favor Alpgen with low scale Leading jet in Z + jet + XSecond jet in Z + 2jet + XThird jet in Z + 3jet + X Phys. Lett. B 669, 278, Phys. Lett. B 678, 45, Phys. Lett. B 682, 370. See also W+jets, CDF, Phys. Rev. D 77, (R).

Soft QCD and Exclusive Production Prerequisites for High Pt Physics Monte Carlo Tuning Exclusive Higgs Production at the LHC

Particle Production in Non-Diffractive Inelastic Events  Particle production in “soft” collisions  Interesting soft QCD  Important for MC tunings Complement the underlying event study in hard-scattering events Actively used for recent MC tunes  Early physics from the LHC January 18, Phys. Rev. D 79,

Exclusive Production  Attractive channel for Higgs physics at the LHC  At the Tevatron, the cross section too small Study similar channels to “calibrate” theory prediction January 18, Reliable calculations from Khoze, Martin, and Ryskin. Eur. Phys. J C14,525(2000). Phys. Rev. D 77,

January 18, Summary & Remarks Tremendous progress has been made to advance understanding of QCD at the Tevatron  Determination of α s and PDFs from jet x-section measurements  Photon + c-jet measurement challenge theorists  Z/W+jet(s) measurements test pQCD, help MC modeling and Higgs/BSM searches  Soft QCD interactions and Underlying event measurements important for MC tuning  Tevatron exclusive production measurements provide basis to LHC exclusive Higgs studies  Much more to come - Tevatron expects ~12 fb -1 by 2011

January 18, Acknowledgement  Many thanks to: S. Pronko, C. Mesropian, D. Bandurin, S. Lammers, D. Lincoln, A. Bhatti, J. Dittmann, …

Backup

January 18, Z+b-jets Production  Probe the not well-known b-content of the proton  Backgrounds for SM Higgs Search (ZH  ννbb) and SUSY Both electron and muon channels Jets with Et > 20 GeV and |  | < 1.5 Data and theory in agreement but both have sizable uncertainties (No complete NLO prediction for Z+bb) Large variations between MC models (important inputs for tuning) Phys. Rev. D79, (2009)

January 18, Jet Production and Measuremnt HAD EM Calorimeter-level jets Underlying event Hadronic showers EM showers Hadron-level jets Parton-level jets Hadronization Unfold measurements to the hadron (particle) level Correct parton-level theory for non-perturbative effects (hadronization & underlying event) Jets are collimated spray of particles originating from parton fragmentation.  To be defined by an algorithm

January 18, Midpoint cone-based algorithm  Cluster objects based on their proximity in y-  space  Starting from seeds (calorimeter towers/particles above threshold), find stable cones (kinematic centroid = geometric center).  Seeds necessary for speed, however source of infrared unsafety.  In recent QCD studies, we use “ Midpoint ” algorithm, i.e. look for stable cones from middle points between two adjacent cones  Stable cones sometime overlap  merge cones when p T overlap > 75% Jet “Definitions” – Jet Algorithms Infrared unsafety: soft parton emission changes jet clustering More advanced algorithm(s) available now, but negligible effects on this measurement.

January 18, Jet “Definitions” – Jet Algorithms k T algorithm Cluster objects in order of increasing their relative transverse momentum (k T )  until all objects become part of jets D parameter controls merging termination and characterizes size of resulting jets No issue of splitting/merging. Infrared and collinear safe to all orders of QCD. Every object assigned to a jet: concerns about vacuuming up too many particles. Successful at LEP & HERA, but relatively new at the hadron colliders  More difficult environment (underlying event, multiple pp interactions…)

January 18, Inclusive Jet Cross Section  Test pQCD over 8 order of magnitude in dσ 2 /dp T dy  Highest p T jet > 600 GeV/c  Jet energy scale (JES) is dominant uncertainty: CDF (2-3%), D0 (1-2%)  Spectrum steeply falling: 1% JES error  5—10% (10—25%) central (forward) x-section p T (GeV/c) Phys. Rev. D 78, (2008) p T (GeV/c) Phys. Rev. Lett. 101, (2008)

January 18, Inclusive Jets with Kt Algorithm  Data/theory comparison consistent between measurements with cone and Kt algorithms and with different D values (jet sizes) Phys. Rev. D 75, (2007)

January 18,  apply this correction to the pQCD calculation  to be used for future MSTW/CTEQ PDF results  first time consistent theoretical treatment of jet data in PDF fits 32 From Particle to Parton Level use models to study effects of non-perturbative processes (PYTHIA, HERWIG) hadronization correction underlying event correction CDF study for cone R=0.7 for central jet cross section new in Run II !!!

January 18, Midpoint vs SIScone: hadron level  Differences between the currently-used Midpoint algorithm and the newly developed SIScone algorithm in MC at the hadron-level.

January 18, Midpoint vs SIScone: parton level  Differences between the currently-used Midpoint algorithm and the newly developed SIScone algorithm at the parton-level. Differences < 1% → negligible effects on data-NLO comparisons

January 18, Inclusive Jets: Cone vs Kt Algorithms Midpoint Cone AlgorithmkT Algorithm

January 18, PDF with Recent Tevatron Jet Data  Tevatron Run II data lead to softer high-x gluons (more consistent with DIS data) and help reducing uncertainties  MSTW08 does not include Tevatron Run 1 data any longer while CT09 (CTEQ TEA group) still does, which makes MSTW08 high-x even softer (consistent within uncertainty) MSTW08: arXiv: , Euro. Phys. J. C CT09: Phys.Rev.D80:014019,2009. W.r.t. MSTW 2008 W.r.t. CTEQ 6.6

January 18, W+b-jets production W+b-jets production Large bkgd for many analyses  SM Higgs (WH) production  Single top quark production  production (See Bernd ’ s and Krisztian ’ s talks.) Can we better understand this bkgd? Both electron and muon channels Jets with Et > 20 GeV and |  | < 1.5 WH →lνbb search Success of NLO QCD. Awaiting for differential measurements. arXiv:

January 18, UE in Jet and Drell-Yan Production Jet production:  Transverse region sensitive to UE  High statistics jet sample  Studies in various dijet topologies DY production:  Transverse and toward regions (excluding lepton-pairs) sensitive to UE  Cleaner environment (Z/γ* carries no color)  Limited statistics Leading jet / Z Direction jet, γ, Z jet Transverse plane  -  Plane Underlying Event: everything except hard scatter

January 18, UE in DY and Jet Production Comparisons of three regions  Away region p T density goes up with lepton-pair p T, while the transverse and toward region p T densities are mostly flat with lepton-pair p T Comparisons between jet and DY  Similar trend in jet and DY events: UE universality?  Tuned Pythia describe data reasonably well. There are many more plots for UE in jet and Drell-Yan production corrected to hadron level: Very important for MC generator tuning/development

January 18, Double Parton using γ+3 Jets Double Parton using γ+3 Jets  Study interactions of two parton pairs in single proton: Insight to parton spatial distributions in the proton Background to other process especially at high luminosities Main background signal σ DP = σ γj σ jj /σ eff σ eff : effective interaction region (Large σ eff : partons more uniformly distributed)

January 18, Double Parton Scattering σ eff = 15.1±1.9 mb (consistent with previous CDF results.)  Calculated for the pair that gives the minimum value of S: D0 Note 5910